In the care of wounds inflicted in an operation or by injury and at risk of infection, plastic implants which contain antibiotic drugs and release them continuously over a specific period of time are often used. For certain indications, small drug-containing plastic bodies drawn onto surgical wires or threads in the manner of a string of beads have proven successful (German Patent 23, 20 373, German Patent 26 51 441, European Patent 0 157 909, European Patent 0 157 910, incorporated herein by reference).
An advantage of these chains of small drug-containing bodies in comparison with other implants for the local release of active substance is that the surgeon can make an adjustment according to the size of the site of the wound and the requirement for active substance by simply cutting the chains to length. A further advantage is that, after the end of therapy or once the chains are depleted, they can be removed in one piece from the body area in a comparatively simple operation. Generally serving as the polymer matrix for the small drug-containing bodies are polymer materials based on poly(meth)acrylates.
The industrial production of such chains of small drug-containing plastic bodies takes place by extruding a mixture of powdered or granulated poly(meth)acrylate polymer and the pharmaceutical active substance as well as further additives, if appropriate, and molding it by the injection-molding process in a mold to form, for example, small spherical bodies, these being intermittently injection-molded onto a thread or wire passed through the mold.
For production technology reasons, commercial reasons and, not least, licensing reasons, industrially produced implants in the form of strings of beads cannot be offered with just any desired pharmaceutical active substances or in just any desired amounts. However, over and above the ready-made products charged with a predetermined amount of active substance, surgeons often have a need to carry out therapy with implants of this type which allow an individual selection, combination or adjustment of active substance. This can be accomplished by producing such implants themselves before or during the operation, in which case the active substance is formulated according to case-specific specifications.
The use of bone cement based on poly(meth)acrylate polymer as a matrix material for drug-containing implants is known. Bone cements are self-setting mixtures which generally comprise essentially a powdered solid component of poly(meth)acrylate and a liquid component of a (meth)acrylate. By mixing these components, it is possible to obtain compositions of low to high viscosity which, due to the presence of polymerization initiators, cure within a period of time of typically about 10-20 minutes. Such mixtures, mixed with pharmaceutical active substances, may likewise serve for producing drug-containing implants, the not yet cured composition being injected into corresponding molds. This production variant is suitable for manual production, in particular the processing time of the bone cement mixture is only short.